1. Field of the Invention
The present invention relates to control of a chopper of a motor for railway vehicles. More specifically, the invention relates to a method and a system for controlling a chopper adapted to preventing the wheels from slipping during a traction mode and sliding during a braking mode and to increasing the tractive and braking force to a limit of adhesion between the wheels and the rails, in order to obtain good acceleration characteristics.
2. Description of the Prior Art
When a D.C. motor is driven through a chopper, in general, the constant-current control is carried out in order to obtain a constant acceleration. The constant-current control is continued even when the wheel axle undergoes the slipping and sliding. To prevent this, therefore, a method has been employed to detect the slipping and sliding, and to suppress the current command. The detection means consists of detecting the slipping and sliding depending upon the voltage differences or speed differences among a plurality of axle motors or depending upon the speed difference from that of the unforced axles, thereby to reduce the command current.
According to the above-mentioned prior art in which the slipping and sliding are detected relying upon the voltage difference or speed difference, and the difference is processed to decrease the command, however, the control lag is necessarily involved. Furthermore, a dead band of a given width must be provided to cope with error in the wheel diameter involving the control lag, too. Therefore, the response is not sharp for the slipping and sliding and, accordingly, limitation is imposed on the control performance.